Highly stable single-crystal LaB6 cathode for conventional electron microprobe instruments

Abstract

The performance of single-crystal LaB6 cathode was examined by measuring the brightness and current stability under the same conditions as for the conventional W hairpin cathode. The LaB6 cathode was mounted in Vogel-type electron gun assembly of an electron probe microanalyser JAX-3 specifically modified for this purpose. The result shows that the present LaB6 cathode provides not only high brightness of 2×105 A/cm2 str. at 20 kV, but also high-current stability better than 1×10−3 Ah−1 in standard operation without any specific aid for current stabilization. Thus an order of magnitude increase in both the brightness and service lifetime can easily be obtained provided that the vacuum of the system is adequate, namely better than 1×10−5 Torr (1.33×10−3 Pa). This substantial improvement of the present single-crystal LaB6 cathode over the conventional W hairpin was also confirmed in a practical way by use in a commercial-type scanning Auger electron microscope, JAMP III.